1. Field of the Invention
This invention relates to a process for the lamination of a vinyl film to a cellulosic substrate and to laminated products produced thereby. More particularly, this invention relates to a process for the formation of a vinyl film-cellulosic substrate laminate wherein a novel multi-layer lamination adhesive process is utilized.
2. Prior Art
Numerous adhesives have been proposed for use in laminating vinyl films to cellulosic substrates. However, various shortcomings exist with many such adhesives. Thus, proteinaceous materials while being relatively inexpensive and characterized by good adhesive properties are highly susceptible to water. Organic solutions of polyacrylates are flamable, toxic and cause product swelling or solvation of the vinyl plastic.
Vinyl acetate-ethylene emulsion adhesives have been proposed for use in connection with vinyl surfaces. The use of such emulsion adhesives is particularly attractive since emulsion adhesives provide an at least partially water-born system thereby minimizing the use of volatile organic solvents which provide environmental hazards. However, the vinyl acetate-ethylene emulsion adhesives have often suffered from inadequate bond performance when used to produce vinyl film-cellulosic substrate laminates and particularly in connection with those laminates formed in a continuous hot-line heat reactivated laminating process.
U.S. Pat. No. 4,152,313 to O. Fogle, J. Cooley and M. E. Taylor describes a vinyl acetate-ethylene emulsion adhesive comprising toluene and an N-lower alkyl substituted pyrrolidone. Such adhesive provides improved bond strength and has been found suitable for use in continuous hot-line heat reactivated laminating processes.
However, the use of aqueous-based emulsion adhesives on cellulosic substrates can cause a rise or swelling of the surface of the cellulosic substrate. Accordingly, it would be highly desirable to provide a polymeric emulsion adhesive system which avoids such swelling and which increases strength of the adhesive.